<%@ page import="java.util.ArrayList" %>
<%@ page import="java.util.HashMap" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

    <%
//        1、值为 null 值的时候，为空
        request.setAttribute("emptyNull",null);
//        2、值为空串的时候，为空
        request.setAttribute("emptyString","");
//        3、值是 Object 类型数组，长度为零的时候
        request.setAttribute("emptyArray",new Object[]{});
//        4、list 集合，元素个数为零
        request.setAttribute("emptyList",new ArrayList<Object>());
//        5、map 集合，元素个数为零
        request.setAttribute("emptyMap",new HashMap<String,Object>());
    %>

    ${ empty emptyNull} <br>
    ${ empty emptyString} <br>
    ${ empty emptyArray} <br>
    ${ empty emptyList} <br>
    ${ empty emptyMap} <br>

    <hr>
    ${12 != 12 ? "国哥帅呆了" : "国哥又骗人了"}
</body>
</html>
